Fire suppression system with improved two-phase flow distribution

ABSTRACT

A two-phase liquid/inert gas flow inerting fire suppression system is provided having improved liquid fire suppressant distribution within the inert gas flow. The system includes a flow distribution network having a first pipe interconnected with a second pipe at a flow splitting tee. A liquid flow redistribution device is disposed in the first pipe upstream with respect to fluid flow of the flow splitting tee.

FIELD OF THE INVENTION

This invention relates generally to fire suppression systems. Moreparticularly, this invention relates to improved liquid distributionwithin the two-phase flow distribution network in an inerting firesuppression system.

BACKGROUND OF THE INVENTION

Fire suppression systems are commonly used in commercial buildings forextinguishing fires. In one type of fire suppression system, a jet ofliquid fire extinguishing agent, most commonly water from a water supplytank, is injected into a high velocity stream of pressurized inert gasfrom an inert gas storage tank as the inert gas passes through a supplypipe forming part of a network of distribution pipes communicating witha network of discharge nozzles mounted to the distal ends of therespective distribution pipes. Upon interaction of the high velocitystream of inert gas with the water jet, the water droplets in the waterjet are atomized into a mist of very small or minute droplets, therebyforming a two-phase mixture of water mist droplets entrained in andcarried by the inert gas stream. This two-phase mixture is distributedvia the network of distribution pipes to the discharge nozzles that areoperatively associated with the region to be protected. The dischargenozzles distribute the water mist droplets and inert gas over a desiredarea to flood that area with water mist droplets and inert gas toextinguish a fire in the protected region.

The inert gas commonly used in conventional inerting fire suppressionsystems is nitrogen, but argon, neon, helium, carbon dioxide or otherchemically non-reactive gas, or mixtures of any two or more of thesegases may be used. The inert gas suppresses fire within the protectedregion by diluting the oxygen content within the protected region andalso increasing the heat capacity per mole of oxygen within theprotected region thereby raising the overall heat capacity of theatmosphere within the protected volume. Due to the presence of the waterdroplets, the two-phase mixture of water mist droplets and inert gas hasa higher overall local heat capacity than the inert gas alone.Consequently, the two-phase mixture of water mist droplets and inert gaswill more effectively absorb heat from the flame to the point that thetemperature of the gas within the vicinity of the flame sheath dropsbelow a threshold temperature below which combustion can not besustained. International Patent Application No. PCT/GB02/01495,published as International Publication WO02/078788, for example,discloses a fire and explosion suppression system of the typehereinbefore described.

In such two-phase fire suppression systems, non-homogenous distributionof water mist droplets within the two-phase mixture of water mistdroplets and inert gas flowing through the fluid distribution networkmay occur. In long horizontally extending stretches of pipe within thefluid distribution network, the water mist droplets may not be evenlydistributed in the gas flow. For example, the water mist droplets mayhave a tendency to concentrate in the lower half of the two-phase flowpassing therethrough. When a pipe junction is reached whereat thetwo-phase is divided, it is desired that the water mist droplets bedivided proportionally with the split of the inert gas flow as it passesfrom the inlet pipe to the junction into the two outlet pipes leadingfrom the junction, thereby maintaining a constant mass flow ratio ofliquid to gas. However, if the water mist droplets are not relativelyuniformly distributed in the flow entering the junction, the water willnot proportionally distribute between the respective inert flowsdischarging through the junction. Such a disproportionate distributionof water between the respective downstream streams could result in somespray nozzles being supplied with an excessive amount of water whileother spray nozzles are under supplied.

SUMMARY OF THE INVENTION

A fire suppression system for extinguishing a fire in a protected spaceincludes a plurality of fluid discharge devices disposed in operativeassociation with the protected space, and a flow distribution networkfor directing a flow of the inert gaseous fluid and liquid fireextinguishing agent, such as water or other fire extinguishing liquid,to the plurality of fluid discharge devices. The flow distributionnetwork includes a first pipe interconnected in fluid communication witha second pipe at a flow splitting tee having an inlet leg for receivingfluid flow from the first pipe, a first outlet leg for discharging afirst portion of the received fluid flow to a first segment of thesecond pipe, and a second outlet leg for discharging a second portion ofthe received fluid flow to a second segment of the second pipe. Theliquid fluid flow redistribution device is disposed in the first pipeupstream with respect to fluid flow of the flow splitting tee.

In an embodiment, the liquid fluid flow redistribution device comprisesa swirler device for imparting rotation to the liquid fluid flow passingthrough the first pipe.

In an embodiment, the liquid fluid flow redistribution device comprisesan annular ring member having a circumferential base having a pluralityof flow openings extending therethrough and a cylindrical flangeextending axially outwardly from a radially inward portion of theannular ring member. The annular ring is disposed coaxially in the firstpipe with an outer circumferential rim of the base in contact with aninner wall of the first pipe and the inner cylindrical flange extendingaxially upstream with respect to fluid flow through the first pipe.

In an embodiment, the liquid fluid flow redistribution device comprisesa ramp extending circumferentially about and outwardly from an innerwall of the first pipe, with the ramp extending at an inward inclinationin a downstream direction with respect to fluid flow through the firstpipe. In an embodiment, the liquid fluid flow redistribution devicecomprises a recessed cavity formed in and extending circumferentiallyabout an inner wall of the first supply pipe.

In an embodiment, the liquid fluid flow redistribution device comprisesa venturi scoop device disposed coaxially within the first pipe andincluding a central passage therethrough having a throat section anddisposed coaxially within the first pipe in spaced relationship with aninner wall of the first pipe so as to form a cavity between the innerwall and the channel member. A plurality of fluid flow openings areprovided in the throat of the venturi device that pass through thechannel member to establish fluid flow communication between the cavityand the central passage through the channel member. The venturi scoopdevice may comprise a longitudinally elongated shell defining a throat,a converging section extending axially in an upstream direction from thethroat and a divergent section extending axially in a downstreamdirection from the throat.

In an embodiment, the liquid fluid flow redistribution device comprisesa first perforated circular disc is disposed in the first pipeimmediately upstream with respect to fluid flow of the inlet to the flowsplitting tee. In an embodiment, a second perforated disc is disposed inthe second pipe immediately downstream of the first outlet of the flowsplitting tee, and a third perforated disc is disposed in the secondpipe immediately downstream of the second outlet of the flow splittingtee.

In an embodiment, a flow turbulence generating device may be disposed ineach of the second pipes downstream with respect to fluid flow of theflow splitting tee. In an embodiment, the flow turbulence generatingdevice may be at least one vortex generating device. In an embodiment,the flow turbulence generating device may be a venturi device insertedin the pipe.

In an embodiment, a tubular liner may be disposed within the first pipeupstream with respect to fluid flow of the first perforated plate at theinlet to the flow splitting tee. The tubular liner has an outsidediameter smaller than the inside diameter of the first pipe, whereby afirst annular flow passage is defined between the tubular liner and thefirst pipe and a second inner passage is defined within and extendingaxially through the tubular liner. The inert gas flows through both thefirst annular flow passage and the second inner flow passage, while thewater, or other liquid fire extinguishing agent, is only admitted intothe inert gas flowing through the inner passage. A plurality of openingsare provided in the tubular liner to define a plurality of flow passagesthrough which inert gas may pass from the first annular flow passageinto the inner flow passage to penetrate into the two-phase flow ofwater and inert gas passing through the inner flow passage. The openingsin the tubular liner may be arranged at axially spaced intervals alongthe tubular liner and at circumferentially spaced intervals about thetubular liner, as desired. The openings may also be arranged in discretesets of openings as desired.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the invention is to be read inconnection with the accompanying drawing, where:

FIG. 1 is a depiction, partly is schematic and partly in perspective, ofa first exemplary embodiment of an inerting fire suppression system inaccord with the invention;

FIG. 2A is a depiction in perspective of a first embodiment of a flowsplitting tee of the inert gas distribution network shown in FIG. 1;

FIG. 2B is a depiction in perspective of a second embodiment of a flowsplitting tee of the inert gas distribution network shown in FIG. 1;

FIG. 3 is a perspective view of a first exemplary embodiment of a liquidflow redistribution device;

FIG. 4 is a perspective view of a second exemplary embodiment of aliquid flow redistribution device;

FIG. 5 is a perspective view of a third exemplary embodiment of a liquidflow redistribution device;

FIG. 6 is a perspective view of a fourth exemplary embodiment of aliquid flow redistribution device;

FIG. 7 is a perspective view of a fifth exemplary embodiment of a liquidflow redistribution device;

FIG. 8 is a depiction, partly is schematic and partly in perspective, ofa second exemplary embodiment of an inerting fire suppression system inaccord with the invention;

FIG. 9 is an elevation view, partly in section, of a first exemplaryembodiment of a portion of the inert gas distribution network of FIG. 8upstream and downstream of the flow splitting tee;

FIG. 10 is a perspective view of a sixth exemplary embodiment of aliquid flow redistribution device; and

FIG. 11 is an elevation view, partly in section, of a second exemplaryembodiment of a portion of the inert gas distribution network of FIG. 8upstream and downstream of the flow splitting tee.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 and 8, in particular, there are depicted firstand second exemplary embodiments, respectively, of a two-phase inertingfire suppression system 10. Each of the exemplary embodiments of thefire suppression system 10 includes one or more vessels 20 for storingan inert gas, that is a chemically non-reactive gas, such as nitrogen,argon, neon, helium, or a mixture of two or more of these gases, a waterstorage vessel 30, and at least one discharge device 40 disposed withinthe region to be protected. However, except when the region to beprotected is a single rather small room, a plurality of dischargedevices would generally be provided within the region to be protected,with one or more discharge devices provided per room defined within theprotected region.

The inert gas storage vessels 20 are connected in parallel arrangementin flow communication with the spray nozzle assemblies 40 via an inertgas distribution network made of a supply pipe 15, an intermediatedistribution pipe 17 and a plurality of circuit pipes 19. The inert gassupply pipe 15 at its terminus is in fluid flow communication with theintermediate distribution pipe 17. Each of the circuit pipes 19 branchesoff from and is in fluid flow communication with the intermediatedistribution pipe 17 and has a terminus disposed within the space to beprotected to which a respective one of the spray nozzles is mounted. Aswill be explained in further detail later, when a fire is detectedwithin the space to be protected, inert gas under pressure within theinert gas vessels 20 passes therefrom through the supply pipe 15 to andthrough the intermediate distribution pipe 17 and thence to and througheach of the circuit pipes 19 which feed the inert gas to a respectiveone of the spray nozzle assemblies 40.

Each of the inert gas storage vessels 20 has its gas outlet connectedvia a branch supply line 13 in flow communication with the supply pipe15. A check valve 14 may be disposed in each branch supply line 13 forallowing the inert gas to flow from the respective inert gas storagevessel 20 associated therewith through branch supply line 13 into theinert gas supply pipe 15, but not to flow back into the inert gasstorage vessel. Each of the inert gas storage vessels 20 may be equippedwith an outlet valve 16 to regulate the gas discharge pressure. Ifdesired, the outlet valve 16 may also be designed to control the rate ofinert gas flow from the storage vessel associated therewith.

In the depicted embodiment, the supply pipe 15 and the intermediatedistribution pipe 17 intersect in a T-shaped arrangement with the supplypipe 15 connected to the inlet leg 52 of the bull tee 50 and segments17A and 17B of the intermediate distribution pipe 17 connected to therespective two outlet legs 54, 56 of the bull tee 50, as illustrated inFIG. 2A. In the depicted embodiment, the circuit pipe 19A intersects theintermediate distribution pipe 17 in a T-shaped arrangement with theupstream segment 17A of the intermediate distribution pipe 17 connectedto the inlet leg 62 of the tee 60 and the downstream segment 17C of theintermediate distribution pipe 17 connected to one outlet leg 64 of theside tee 60 and the circuit pipe 19A connected to the other outlet leg66 of the side tee 60, as illustrated in FIG. 2B.

The two-phase fluid received from the inert gas supply pipe 15 throughthe inlet leg 52 of the bull tee 50 splits into two portions, oneportion discharging through the first outlet leg 54 of the bull tee 50into segment 17A of the intermediate distribution pipe 17 and the otherportion discharging through the second outlet leg 56 of the bull tee 50into segment 17B of the intermediate distribution pipe 17. The two-phasefluid received from the upstream segment 17A of the intermediatedistribution pipe 17 through the inlet leg 62 of the side tee 60 splitsinto two portions, one portion discharging through the first outlet leg64 of the side tee 60 into the circuit pipe 19A and the other portiondischarging through the second outlet leg 66 of the side tee 60 intodownstream segment 17C of the intermediate distribution pipe 17.

The water storage vessel 30 defines an interior volume 32 wherein asupply of water is stored. A gas inlet line 34 establishes flowcommunication between the inert gas supply pipe 15 and an upper regionof the interior volume 32 of the water storage vessel 30. A water outletline 36 establishes flow communication between a lower region of theinterior volume of the water storage vessel 30 and the inert gasdistribution network at a location downstream with respect to inert gasflow of the location at which the gas inlet line 34 taps into the inertgas supply line 15. Additionally, a flow restriction device 38 may bedisposed in the inert gas distribution network at a location between thelocation upstream thereof at which the gas inlet line 34 taps into thesupply line 15 and the location downstream thereof at which the wateroutlet line 36 opens into the inert gas distribution network. The flowrestriction device 38, which may, for example, comprise a fixed orificedevice interdisposed in the inert gas supply line 15, causes a pressuredrop to occur as the inert gas traverses the flow restriction device 38,whereby a gas pressure differential is established between the upstreamlocation at which the gas inlet line 34 taps into the inert gas supplypipe 15 and the downstream location at which the water outlet line 36opens into the inert gas distribution network.

A spray nozzle 37 may be mounted to the outlet end of the water outletline 36 to atomize or otherwise produce a mist of water droplets as thewater from the supply tank 30 is introduced into the inert gas flow. Inthe embodiment of the fire suppression system 10 depicted in FIG. 1, thewater outlet line 36 opens into a mixing chamber 35 disposed in theinert gas supply pipe 15 of the inert gas distribution network at alocation downstream with respect to gas flow of the flow restrictiondevice 38. However, it is to be understood that a defined mixing chamber35 is not required to carry out the invention. Rather, as in theembodiment of the fire suppression system 10 depicted in FIG. 8, thewater outlet line 36 may discharge directly into the interior volumedefined by the inert gas supply pipe 15 with the water from the watertank 30 passing from the water outlet line 36 through spray nozzle 37directly into the inert gas flow passing through the supply pipe. Thespray nozzle 37 converts the water into a mist of droplets and spraysthe droplets into the flow of inert gaseous fluid passing through themixing chamber 35 or the inert gas supply pipe 15, thereby forming atwo-phase fluid flow which continues through the supply pipe 15 and theremainder of the flow distribution network to the plurality of spraynozzles 40. A flow control device 33 may be disposed in the water outletline 36 to regulate the amount of water flowing therethrough.

The length of travel of the two-phase flow from the point of injectionof the water into the inert gas through section 15C of the inert gassupply pipe 15 to its passing into the intermediate distribution pipe 17for distribution amongst the various spray nozzles 40 via the respectivecircuit pipes 19 may be several meters, for example up to 20 or moremeters depending upon the system design. In the course of traversingthis path through section 15C of the inert gas supply pipe 15, the waterdroplets and inert gas may separate to varying degree. In someinstances, the water droplets may coalesce and concentrate as a liquidfilm flowing along the inner wall defining the flow passage of section15C of the gas supply pipe 15 forming a tunnel about a core flow ofinert gas. In other instances, particularly in horizontal runs of pipe,the water droplets may concentrate primary along a lower arc portion ofthe wall with the inert gas flowing thereover. In still other instances,the water droplets may concentrate in a plug flow along the axis ofsupply pipe with the inert gas flowing circumferentially about the flowof water droplets.

At each of the pipe intersections within the fluid distribution network,the incoming two-phase fluid flow is split into two ongoing flows. Forexample, the two-phase fluid received through the inlet leg 52 of thebull tee 50 splits into two portions, one portion discharging throughthe first outlet leg 54 of the bull tee 50 into segment 17A of theintermediate distribution pipe 17 and the other portion dischargingthrough the second outlet leg 56 of the bull tee 50 into segment 17B ofthe intermediate distribution pipe 17. In conventional two-phase flowinerting systems, because the distribution of the liquid film on theinner wall of the pipe is generally not uniform as the flow enters theflow splitting tee, the potential exists for an unequal distribution ofthe liquid phase to occur between the two-phase flows discharging fromthe flow splitting tee. Applicants have determined that the occurrenceof such an unequal distribution of liquid phase between the two outgoingflows may be diminished by affecting a redistribution of the liquidphase of the two-phase flow upstream of the flow splitting tee.

To reduce, if not eliminate, the potential for unequal distribution ofthe liquid phase in the outgoing two-phase fluid flows leaving a flowsplitting tee at a pipe intersection in the fluid distribution networkof the system 10, a liquid fluid flow redistribution device 70 isdisposed in the particular pipe feeding the two-phase flow to the inletleg of the flow splitting tee at a location upstream of theintersection. For example, a liquid fluid flow redistribution device 70may be disposed in the supply pipe 15 downstream with respect to fluidflow of the introduction of the liquid fluid flow into the flow of theinert gaseous fluid passing through the supply pipe 15 and upstream ofthe bull tee 50 to reduce the unequal distribution of the water betweenthe outgoing two-phase fluid flows at the bull tee 50. In an embodiment,as illustrated in FIG. 1, the liquid flow redistribution device 70 maybe disposed at or within a few pipe diameters of the intersection of thesupply pipe 15 with the intermediate distribution pipe 17. The liquidfluid flow redistribution device 70 functions to provide a more uniformdistribution of water in the fluid flow passing through the supply pipe15 downstream of the device.

Similarly, to reduce, if not eliminate, the potential for unequaldistribution of the liquid phase between the outgoing two-phase fluidflows at the intersection of the intermediate distribution pipe 17 andone or more circuit pipes 19 in the fluid distribution network of thefire suppression system 10, a liquid fluid flow redistribution device 70may be disposed in the intermediate distribution pipe 17. In anembodiment, as illustrated in FIG. 1, the liquid flow redistributiondevice 70 may be disposed at or within a few pipe diameters upstream ofthe side tee 60 defining the intersection of the circuit pipe 19 withthe intermediate distribution pipe 17. At this location, the liquidfluid flow redistribution device 70 functions to provide a more uniformdistribution of water between the flow passing into the circuit pipe 19Aand the flow passing into the intermediate distribution pipe 17Cdownstream of the device.

In an aspect of the invention, the liquid fluid flow redistributiondevice may be any device that when disposed in the two-phase flowpassing through the inert gas distribution network redistributes waterflowing along the inner wall of the pipe into a film distributeduniformly about the circumference of the inner wall of the pipe as theflow enters a flow spitting tee. For example, referring now to FIG. 3,the liquid fluid flow redistribution device may comprise a swirlerdevice 170 having a plurality of curved vanes 172 mounted to an axialshaft 174. In application, the swirler device 170 is disposed in theflow path of the two-phase flow with the shaft 174 aligned along theaxis of the pipe and the outboard edges 176 of the curved vanes 172abutting the inner wall of the pipe, 15, 17. As the flow traverses theswirler device 170, a vanes 172 impart a swirl to the two-phase flow andalso to any water flowing along the inner wall of the pipe, therebyaffecting a channeling of the water as a result of the imparted swirlinto a film distributed uniformly about the circumference of the innerwall of the pipe as the flow traverses the swirler device 170. Thelocation of placement upstream of the pipe intersection defined by theflow splitting tee 50, 60 will generally be at a few pipe diametersupstream from the intersection. The exact placement of the swirlerdevice, as well as the swirler vane dimensions and the swirl angle ofthe vanes 172, may be varied as desired to optimize the effect of theswirl in any particular application.

In another embodiment, as depicted in FIG. 4, the liquid fluid flowredistribution device may comprise an annular ring member 270 having acircumferential washer-like base 272 and a flange 274 extending axiallyoutward from a face of the base 272 along the inner circumference of thebase 272. The annular ring member 270 is positioned within the pipe 15,17 with the outer circumferential rim of the base 272 abutting the innerwall of the pipe 15, 17 and with the flange 274 extending in theupstream direction with respect to fluid flow through the pipe in spacerelationship with the inner wall of the pipe thereby forming acircumferential channel between the flange and the inner wall of thepipe. A plurality of openings 275 are provided in and extend through thebase 272 outboard of the flange 274 to provide a plurality of flowopenings therethrough. In operation, water flowing along the inner wallof the pipe from the upstream direction collects in the circumferentialchannel and passes through the openings 275 to form a film of waterdistributed uniformly about the circumference of the inner wall of thepipe about a core flow of two-phase flow of water droplets and inert gaspassing through the central opening 277 of the annular ring member 270.Although shown as a plurality of circular holes disposed at uniformlyspaced circumferential intervals about the base 272, it is to beunderstood that the openings 275 may be slots or of other shape, andthat the number, size and spacing of the openings 275 may be varied asdesired to optimize the effect of the annular ring member 270 in anyparticular application.

In another aspect of the invention, the liquid fluid flow redistributiondevice may be any device that when disposed in the two-phase flowpassing through the inert gas distribution network redirects waterflowing along the inner wall of the pipe into the core two-phase flowingof water droplets and inert gas flowing through the pipe. For example,referring now to FIGS. 5 and 6, the liquid fluid flow redistributiondevice 70 may comprise a discontinuity in the inner wall of the pipethat results in turbulent eddies or unsteady vortex shedding of liquidpassing along the inner wall as it traverses the discontinuity. As aresult of the turbulence generated, the water departs from the innerwall as it traverses the discontinuity and is re-entrained in the coretwo-phase flow passing through the pipe.

For example, the liquid fluid flow redistribution device may comprise anannular recessed cavity 370 extending in a band-like fashion about thecircumference of the inner wall of the pipe 15, 17 as depicted in FIG.5. When the water flowing along the inner wall of the pipe encountersthe upstream lip 372 of the recessed cavity 370, the water flows intothe cavity 370 and then encounters the downstream lip 374 of therecessed cavity when exiting the cavity. The water sheds off thedownstream lip 374 of the cavity 370 and, rather than reattaching toinner wall of the pipe, is re-entrained in the core two-phase flow dueto the turbulence of the unsteady vortex eddies generated by thediscontinuity in the surface of the inner wall created by the annularrecessed cavity 370.

In another embodiment, the liquid fluid flow redistribution device maycomprise a ramp 470 extending in band-like fashion about thecircumference of the inner wall of the pipe 15, 17 as depicted in FIG.6. When the water flowing along the inner wall of the pipe encountersthe ramp 470, the water flows along the inwardly inclined surface of theramp. As the water leaves the downstream lip 472 of the ramp, ratherthan reattaching to inner wall of the pipe, the water is re-entrained inthe core two-phase flow due to the turbulence of the unsteady vortexeddies generated by the discontinuity in the surface of the inner wallcreated by the ramp 470. Additionally, the inward inclination of theramp 470 serves to redirect the flow of water away from the wall andinto the core flow of two-phase fluid passing through the pipe 15, 17.

In yet another embodiment, the liquid fluid flow redistribution devicemay comprise a venturi scoop device 570 such as depicted in FIG. 7. Theventuri scoop device 570 includes a longitudinally extending body 572defining a throat section 571 and disposed axially within the pipe 15,17 in spaced relationship with the inner wall of the pipe therebyforming a cavity 573 between the inner wall of the pipe and the outerwall of the body 572. The downstream end of the cavity 573 is closed byan annular ring 574 abutting the downstream end of the body 572. Aplurality of support members 576, typically 2, 3 or 4 in number, extendradially between the outer wall of the body 572 and the inner wall ofthe pipe to support the body 572 therefrom. A plurality of openings 575are provided at circumferentially spaced intervals about and extendthrough the throat section 571 that provide flow passages linking thecavity 573 in fluid communication with the flow passage through thethroat section 571.

When the water flowing along the inner wall of the pipe encounters theventuri scoop 570, the water collects in the cavity 573. As the coreflow of two-phase fluid passes through the throat section 571, a lowpressure zone is created at the throat of the venturi section. As aresult of the pressure differential between the cavity 573 and the lowpressure zone within the throat section 571, water collecting in thecavity 573 discharges therefrom through the plurality of openings 575and is re-entrained in the core two-phase flow. Although shown as aplurality of circular holes disposed at uniformly spaced circumferentialintervals about the throat of the throat section 571, it is to beunderstood that the openings 575 may be slots or of other shape, andthat the number, size and spacing of the openings 575 may be varied asdesired to optimize the effect of the venturi scoop device 570 in anyparticular application.

In an embodiment of the fire suppression system, perforated discs 80A,80B, 80C are disposed in the two-phase flow streams entering and leavingthe flow splitting tee 50 to promote a more uniform distribution of thetwo-phase flow 7 leaving the flow splitting tee 50. Referring now toFIG. 9, a perforated circular disc 80A is disposed in the distributionpipe 17A immediately downstream with respect to fluid flow of the outletof the flow splitting tee opening to the distribution pipe 17A, aperforated circular disc 80B is disposed in the distribution pipe 17Bimmediately downstream with respect to fluid flow of the outlet of theflow splitting tee opening to the distribution pipe 17B, and aperforated circular disc 80C is disposed in the supply pipe 15Cimmediately upstream with respect to fluid flow of the inlet to the flowsplitting tee opening to the supply pipe 15C. Referring now to FIG. 10,each of the circular discs 80 is perforated with a plurality of openings85, such as but not limited to a plurality of circular holes, thatprovide a plurality of discrete flow paths. Each of the openings 85provides a flow restriction through which the two-phase flow must pass.As the two-phase flow traverses the openings 85, each of the individualflow streams undergoes a pressure drop and then expands in turbulenteddies as it exits the opening. The turbulence functions to enhancemixing of the water and inert gas in the two-phase flow. The perforateddiscs 80, in combination, provide a series of pressure drops that theflow must traverse in a very short distance which acts to more evenlydistribute the flow entering the flow splitting tee between the twostreams exiting from the flow splitting tee 50.

The perforated disc 80A disposed upstream of the flow splitting tee 50promotes a more uniform distribution of the two-phase fluid and breaksup any relatively larger water droplets into relatively smallerdroplets. Having passed through the upstream perforated disc 80A andentered the flow splitting tee 50, the two-phase flow impinges on theopposite wall of the tee and splits into two flows passing out of thetee 50 in opposite directions. Each of the perforated plates 80B and 80Cdisposed downstream of the flow splitting tee 50 promotes a more uniformdistribution of the two-phase fluid following the impingement and flowsplitting within the tee 50 and breaks up any relatively larger waterdroplets that may have formed as a result of coalescence of smallerwater droplets due to inelastic collisions of smaller water dropletswithin the flow splitting tee 50.

In addition, vortex generating devices may be disposed in flow path ofthe two-phase flow passing through the supply pipe 15 at a locationupstream of the inlet to the flow splitting tee 50. For example, in theexemplary embodiment depicted in FIG. 9, a series of vortex generatingdevices 92 are disposed at axially spaced intervals along the length ofthe segment 15C of the supply pipe 15 from a location downstream of thepoint at which the water, or other liquid fire extinguishing agent isintroduced into the inert gas flow and a location upstream of theperforate circular disc 80C. As the two-phase flow traverses the vortexgenerating devices 92, unsteady flow vortices are generated in thetwo-phase flow which enhance mixing of the liquid phase and the gasphase to ensure a more uniform distribution of liquid mist dropletsthrough out the inert gas passing into the flow splitting tee 50.

In the exemplary embodiment of the fire suppression system depicted inFIG. 11, an inner tubular liner 60 is disposed coaxially within segment15C of the inert gas supply pipe 15. The inner tubular liner 60 definesan axially elongated inner fluid flow passage 65 bounded by its innerdiameter. The inner tubular liner 60 has an outer diameter that issmaller than the inner diameter of segment 15C of the inert gas supply15. Therefore, an annular flow passage 55 is defined within the inertgas supply pipe 15 between the inner wall of the inert gas supply pipe15 and the outer wall of the inner tubular liner 60. The inner tubularliner 60 extends coaxially within the segment 15C of the inert gassupply pipe 15 from a location downstream with respect to fluid flow ofthe point of injection of water, or other liquid fire extinguishingagent, into the inert gas flow to a location slightly upstream withrespect to fluid flow of the inlet to the flow splitting tee at theintersection of the main supply pipe 15 with the intermediatedistribution pipe 17. For example, the tubular liner 60 may extend from5 to 10 inner diameters of the segment 15C of the inert gas supply pipe15.

Thus, both the annular flow passage 55 defined between the innerdiameter segment 15C of the inert gas supply pipe 15 and the outerdiameter of the tubular liner 60 and the inner passage 65 defined withinthe inner tubular liner 60 open to the upstream portion of the inert gassupply pipe 15 and receive inert gas flow from the upper stream portionof the inert gas supply pipe. A first portion of the inert gas flowpassing through the inert gas supply pipe 15 enters into and traversesthe inner flow passage 65 through segment 15C of the inert gas supplypipe 15 and a second portion of the inert gas passing through the inertgas supply pipe 15 enters into and traverses the annular flow passage 55defined within segment 15C of the inert gas supply pipe. However, thedischarge outlet of the water outlet line 36, or the atomizing nozzle 37if mounted thereto, opens into the inner flow passage 65 at a locationslightly downstream of the mouth 61 of the inner tubular liner 60 of theinert gas supply pipe 15. Thus, the droplets 5 in the mist of water, orother liquid fire extinguishing agent, introduced into the portion ofthe inert gas flow passing through the inner flow passage 65 mixes withthe inert gas 3 to form a two-phase flow 7 of liquid mist dropletsentrained in the inert gas flowing through the inner flow passage 65.Therefore, inert gas 3 only flows through the annular flow passage 55bounded by the inner wall of segment 15C of the inert gas supply pipe 15and the outer diameter of the inner tubular liner 60, while a two-phaseflow 7 of liquid mist droplets entrained in inert gas flows through thefluid flow passage 65 extending axially within the inner tubular liner60.

Additionally, a plurality of openings 67 are provided in the wall of theinner tubular liner 60. The openings 67 provide fluid flow communicationbetween the annular flow passage 55 and the inner flow passage 65defined within the inner tubular liner 60. The openings 60 are arrangedat axially spaced intervals along the length of the tubular liner 60 andat circumferentially spaced intervals about the circumference of thetubular liner 60. In operation of the fire suppression system 10, aportion of the inert gas 3 flowing through the annular flow passage 55passes through each of the openings 67 and into the inner flow passage65 to discharge into and admix with the two-phase flow 7 of liquid andinert gas flowing through the inner flow passage 65. Thus, a series ofjets of inert gas discharge into the two-phase flow at spaced intervalsalong the length of and about the circumference of the inner tubularliner 60. These jets of inert gas serve to break-up any water film thatmay be flowing along the inner wall of the inner tubular liner 60.Additionally, as the inert gas jets penetrate into the two-phase flow,the resulting turbulence in the two-phase flow serves to induce furtherintermixing of the liquid mist droplets and the inert gas to enhanceuniformity in distribution of the liquid droplets in the inert gas flow.

The individual openings 67 or sets of openings 61 may be arranged in anyconfiguration as desired. In the exemplary embodiment depicted in FIG.11, the openings 67 are aligned in two axially extending rows disposeddiametrically opposite each other and are arranged in subgroups 61 ofthree or four openings 67 each with the subgroups 61 axially spacedapart at a desired interval. However, it is to be understood that theparticular arrangement of individual openings 67 or subgroups 61 ofopenings, including but not limited to the number of rows of openings,the circumferential arrangement of the respective rows, the number ofsubgroups within a row, if any, and the number of openings in asubgroup, the spacing between subgroups and individual openings, or anyother facet of the arrangement may be varied as desired for a particularapplication. Further, it is to be understood that the openings 18 may becircular holes, elongated slots or of other shape, and that the size ofthe openings 18 may be varied as desired to optimize performance in anyparticular application.

To reduce, if not eliminate, the potential for unequal distribution ofthe liquid phase in the two-phase fluid flows in the distribution pipes17A and 17B downstream of the respective outlets of the flow splittingtee 50 at the intersection of the inert gas supply pipe 15 and thedistribution pipe 17, an additional flow turbulence generating device,such as for example a venturi device 90 or a vortex generating device92, may be disposed in each of the particular pipes receiving thetwo-phase flow from the flow splitting. For example, in the exemplaryembodiment illustrated in FIG. 9, a vortex generating device 92A isdisposed within the distribution pipe 17A within a few pipe diameters ofthe entrance of the two-phase flow to the distribution 17A from theoutlet leg 54 of the flow splitting tee 50. Similarly, a vortexgenerating device 92B is disposed within the distribution pipe 17Bwithin a few pipe diameters of the entrance of the two-phase flow to thedistribution 17B from the outlet leg 56 of the flow splitting tee 50. Inthe exemplary embodiment illustrated in FIG. 11, a venturi device 90A isdisposed within the distribution pipe 17A within a few pipe diameters ofthe entrance of the two-phase flow to the distribution 17A from theoutlet leg 54 of the flow splitting tee 50. Similarly, a venturi device90B is disposed within the distribution pipe 17B within a few pipediameters of the entrance of the two-phase flow to the distribution 17Bfrom the outlet leg 56 of the flow splitting tee 50.

As the two-phase flows passing from the flow splitting tee 50 traversesthe venturi devices 90 or the vortex generating devices 92, unsteadyflow vortices are generated in the two-phase flow which enhance mixingof the liquid phase and the gas phase to ensure a more uniformdistribution of liquid mist droplets through out the inert gas passingto the spray nozzles 40. As noted previously, coalesced droplets ofwater, or other fire extinguishing fluid, that may have formed as aresult of the inelastic collisions of finer mist droplets, are broken upas a result of the two-phase flow passing through the openings in theperforated circular discs 80A and 80B. Being positioned slightlydownstream of these perforated circular discs, the flow turbulencegenerating devices 90, 92 facilitate the mixing and redistribution ofthe finer droplets resulting from the break-up of the coalesced dropletsinto the inert gas flow.

The inerting fire suppression system of the invention has been describedwith reference to water as the liquid fire extinguishing agent. It is tobe understood that other liquid fire extinguishing agents may be usedinstead of water in the inerting fire suppression system of theinvention. As those skilled in the art will recognize, the teachings ofthe invention may be applied to any two-phase fluid inerting firesuppression system wherein a maldistribution of liquid fireextinguishing agent amongst various branches or circuits of the systemmay potentially occur.

While the present invention has been particularly shown and describedwith reference to the exemplary embodiments as illustrated in thedrawing, it will be understood by one skilled in the art that variouschanges in detail may be effected therein without departing from thespirit and scope of the invention as defined by the claims.

We claim:
 1. A fire suppression system for extinguishing a fire in aprotected space, comprising: a plurality of fluid discharge devicesdisposed in operative association with the protected space; a flowdistribution network for directing a two-phase flow of an inert gaseousfluid and liquid fire extinguishing agent to said plurality of fluiddischarge devices, the flow distribution network including a first pipereceiving the flow of the inert gaseous fluid and liquid fireextinguishing agent and defining a first flow passage interconnected ata flow splitting tee in fluid communication with a second pipe defininga second flow passage and a third flow passage, the flow splitting teehaving an inlet for receiving fluid flow from the first flow passage, afirst outlet for discharging a first portion of the received fluid flowto the second flow passage, and a second outlet for discharging a secondportion of the received fluid flow to the third flow passage; and aliquid fluid flow redistribution device disposed in the first pipeupstream with respect to fluid flow of the flow splitting tee; whereinsaid liquid fluid flow redistribution device comprises an annular ringmember having a circumferential base and a cylindrical flange extendingaxially outwardly from a radially inward portion of the annular ringmember, said annular ring disposed coaxially in the first pipe with anouter circumferential rim of said base in contact with an inner wall ofthe first pipe and said cylindrical flange extending axially upstreamwith respect to fluid flow through the first pipe, said base having aplurality of flow openings formed therein radially outwardly of thecylindrical flange.
 2. A fire suppression system for extinguishing afire in a protected space, comprising: a plurality of fluid dischargedevices disposed in operative association with the protected space; aflow distribution network for directing a two-phase flow of an inertgaseous fluid and liquid fire extinguishing agent to said plurality offluid discharge devices, the flow distribution network including a firstpipe receiving the flow of the inert gaseous fluid and liquid fireextinguishing agent and defining a first flow passage interconnected ata flow splitting tee in fluid communication with a second pipe defininga second flow passage and a third flow passage, the flow splitting teehaving an inlet for receiving fluid flow from the first flow passage, afirst outlet for discharging a first portion of the received fluid flowto the second flow passage, and a second outlet for discharging a secondportion of the received fluid flow to the third flow passage; and aliquid fluid flow redistribution device disposed in the first pipeupstream with respect to fluid flow of the flow splitting tee; whereinsaid liquid fluid flow redistribution device comprises a venturi scoopdevice disposed coaxially within the first pipe, said venturi scoopdevice having a body defining a central passage therethrough having athroat section and disposed coaxially within the first pipe in spacedrelationship with an inner wall of the first pipe so as to form a cavitybetween the inner wall and said body, the body having a plurality offluid flow openings passing therethrough to establish fluid flowcommunication between said cavity and said central passage.
 3. A firesuppression system for extinguishing a fire in a protected space,comprising: a plurality of fluid discharge devices disposed in operativeassociation with the protected space; a flow distribution network fordirecting a two-phase flow of an inert gaseous fluid and liquid fireextinguishing agent to said plurality of fluid discharge devices, theflow distribution network including a first pipe receiving the flow ofthe inert gaseous fluid and liquid fire extinguishing agent and defininga first flow passage interconnected at a flow splitting tee in fluidcommunication with a second pipe defining a second flow passage and athird flow passage, the flow splitting tee having an inlet for receivingfluid flow from the first flow passage, a first outlet for discharging afirst portion of the received fluid flow to the second flow passage, anda second outlet for discharging a second portion of the received fluidflow to the third flow passage; and a liquid fluid flow redistributiondevice disposed in the first pipe upstream with respect to fluid flow ofthe flow splitting tee; wherein said liquid fluid flow redistributiondevice comprises a venturi scoop device disposed coaxially within thefirst pipe, said venturi scoop device having a body defining a centralpassage therethrough having a throat section and disposed coaxiallywithin the first pipe in spaced relationship with an inner wall of thefirst pipe so as to form a cavity between the inner wall and said body,the body having a plurality of fluid flow openings passing therethroughto establish fluid flow communication between said cavity and saidcentral passage; wherein said venturi scoop device disposed coaxiallywithin the first pipe, the body of said venturi scoop device comprises alongitudinally elongated shell having a throat, a converging sectionextending axially in an upstream direction from the throat and adivergent section extending axially in a downstream direction from thethroat.
 4. A fire suppression system for extinguishing a fire in aprotected space, comprising: a plurality of fluid discharge devicesdisposed in operative association with the protected space; a flowdistribution network for directing a two-phase flow of an inert gaseousfluid and liquid fire extinguishing agent to said plurality of fluiddischarge devices, the flow distribution network including a first pipereceiving the flow of the inert gaseous fluid and liquid fireextinguishing agent and defining a first flow passage interconnected ata flow splitting tee in fluid communication with a second pipe defininga second flow passage and a third flow passage, the flow splitting teehaving an inlet for receiving fluid flow from the first flow passage, afirst outlet for discharging a first portion of the received fluid flowto the second flow passage, and a second outlet for discharging a secondportion of the received fluid flow to the third flow passage; and aliquid fluid flow redistribution device disposed in the first pipeupstream with respect to fluid flow of the flow splitting tee, whereinsaid liquid fluid flow redistribution device comprises a firstperforated plate disposed transversely across the first flow passageupstream with respect to fluid flow of the inlet to the flow splittingtee; a second perforated plate disposed transversely across the secondflow passage downstream with respect to fluid flow of the first outletof the flow splitting tee; and a third perforated plate disposedtransversely across the third flow passage downstream with respect tofluid flow of the second outlet of the flow splitting tee; and a firstflow turbulence generating device disposed in the second flow passagedownstream with respect to fluid flow of the first outlet of the flowsplitting tee and a second flow turbulence generating device disposed inthe third flow passage downstream with respect to fluid flow of thesecond outlet of the flow splitting tee; wherein said first and secondflow turbulence generating devices each comprise a vortex generatingdevice.
 5. A fire suppression system for extinguishing a fire in aprotected space, comprising: a plurality of fluid discharge devicesdisposed in operative association with the protected space; a flowdistribution network for directing a two-phase flow of an inert gaseousfluid and liquid fire extinguishing agent to said plurality of fluiddischarge devices, the flow distribution network including a first pipereceiving the flow of the inert gaseous fluid and liquid fireextinguishing agent and defining a first flow passage interconnected ata flow splitting tee in fluid communication with a second pipe defininga second flow passage and a third flow passage, the flow splitting teehaving an inlet for receiving fluid flow from the first flow passage, afirst outlet for discharging a first portion of the received fluid flowto the second flow passage, and a second outlet for discharging a secondportion of the received fluid flow to the third flow passage; a liquidfluid flow redistribution device disposed in the first pipe upstreamwith respect to fluid flow of the flow splitting tee, wherein saidliquid fluid flow redistribution device comprises a first perforatedplate disposed transversely across the first flow passage upstream withrespect to fluid flow of the inlet to the flow splitting tee; and aninner tubular liner having an interior passage disposed coaxially withinthe first pipe and defining an axially extending annular space betweenthe tubular liner and an inner wall of the first pipe, said annularspace defining an annular flow passage and the interior passage of thetubular liner defining the first flow passage, said tubular liner havinga plurality of openings therein establishing fluid flow communicationbetween the annular flow passage and the first flow passage.
 6. A firesuppression system as recited in claim 5 wherein the annular flowpassage comprises a flow passage for conveying inert gas only and thefirst flow passage comprises a flow passage for conveying a two-phasemixture of liquid fire extinguishing agent and inert gas.